In the recent past, it has become known to use, for the purpose of labelling containers, labelling machines comprising ink jet printers which are able to apply information onto a label, or onto a container by direct printing. Normally, printers having a demand-dependent ink jet, so-called “drop-on-demand” printers, are preferably used for this purpose. Since the ink droplets discharged from the nozzles of this type of printers are only those which are actually required for printing, this kind of printer is much more economical than the so-called “continuous-ink” printer in which an ink jet is continuously discharged from the nozzles.
A problem which is characteristic of demand-dependent printers is, however, that the ink in the print head may dry up when the print head is not in use, e.g. when the labelling machine stands still due to a change of shifts or due to some malfunction. Malfunctions may also be caused by a machine which is located upstream or downstream of a labelling machine incorporated in a line. The cleaning or the exchange of the dried-up print head leads to an additional uneconomical downtime.